1. Field of the Invention
The present invention relates to an optical scanning unit module and an optical scanning system for a printer using such a module, and more particularly, to an optical scanning unit module for simultaneously scanning a plurality of beams in different directions, and to an optical scanning system for a printer using such a module.
2. Description of the Related Art
Referring to the printer shown in FIG. 1, a reset device 15, optical scanning units 30, developing units 17, a drying unit 18, and a transfer device 20 are disposed around a circulation path of a photoreceptor belt 14 moving around three rollers 11, 12, and 13.
When printing is performed, the optical scanning units 30 scan light beams to the photoreceptor belt 14. An electrostatic latent image is formed on the photoreceptor belt 14 by the optical scanning units 30 for scanning beams having different color information, and then, the electrostatic latent image is developed by developing solution supplied by the developing units 17 for developing the image using a developer corresponding to the color information of the scanned beam, thus forming a color image on the photoreceptor belt 14. The color image formed on the photoreceptor belt 14 by the developer passes through the drying unit 18, as the photoreceptor belt 14 continues to circulate, and is transferred to a transfer roller 21 rotating by being partially engaged with the photoreceptor belt 14. Subsequently, the image on the transfer roller 21 is transferred to print paper 23 by the rotation of the transfer roller 21 and a press roller 22 with the print paper 23 interposed therebetween.
In the printing operation described above, the four optical scanning units 30 scan beams having color information corresponding to yellow, magenta, cyan, and black colors, respectively.
FIG. 2 shows a conventional optical scanning unit 30, which includes a light source 31, rotary polygon mirror 32, a motor 36, and a lens unit 33. A system controller 35 controls a beam scanning period of the optical scanning units 30 which scan light beams to the photoreceptor belt 14 at a set position in a widthwise direction of the photoreceptor belt 14.
A photodetector 34, which is disposed to receive a light beam scanned beyond the edge of the photoreceptor belt 14, outputs a pulse signal corresponding to a detection of the beam to the system controller 35. The system controller 35 determines a falling edge of the pulse signal as the point in time that the scanned beam reaches the edge of the photoreceptor belt 14, delays emission of a light beam for recording image information until the beam is scanned from the edge of the photoreceptor belt 14 to a set image information recording area D, and then drives the light source 31 to emit the beam for recording the image information.
According to the conventional technology, the system controller 35 controls synchronization of each light source 31 and each motor driver 37 such that the leading edges and positions of the beams scanned by the respective optical scanning units 30 are coincident with the set area of the circulating photoreceptor belt 14. Accordingly, a control circuit for controlling the synchronization of the driving of each motor 36 and each light source 31 is complicated.
In order to overcome the above described complication, it is possible to use a single optical scanning unit and rotate the photoreceptor belt four times for one print. However, the printing speed is lowered by this method. Another solution is to use each reflecting surface of a rotary polygon mirror having a plurality of reflecting surfaces. In other words, a plurality of beams are emitted to different reflecting surfaces of a single rotary polygon mirror, and the beams are reflected by the respective reflecting surfaces to a photoreceptor via an optical means. However, in this method, since optical paths are different for each light beam, an additional controlling means is required to control the beam power and spot size, thereby complicating the system.